This invention relates generally to the electrokinetic mass transfer of medication transdermally and, more specifically, to improved apparatus for the iontophoretic delivery of medication across the membrane formed by the body's skin so the medication can be absorbed by the adjacent tissues and blood vessels.
Iontophoresis has existed for several centuries as a means of applying medication locally through a patient's skin and for delivering medicaments to the eyes and ears. The application of an electric field to the skin was found to greatly enhance the skin's permeability to various ionic agents. The use of iontophoretic techniques has obviated the need for hypodermic injection of medication and medicaments, therby eliminating the concomitant problems of trauma, pain and risk of infection to the patient.
Iontophoresis involves the application of an electromotive force to drive or repel oppositely charged ions through the dermal layers into the area to be treated, either into the surrounding tissues for localized treatment or into the circulatory system for systemic treatment. Positively charged ions are driven into the skin at the anode while negatively charged ions are driven into the skin at the cathode. Studies have shown increased skin penetration of drugs at anodic or cathodic elelctrodes regardless of the predominant molecular ionic charge. This effect is mediated by polarization and osmotic effects. Regardless of the charge of the medicament employed, two electrodes are used in conjunction with the patient's skin to form a closed circuit to promote the penetration or absorption of the medicament on the working electrode.
More recently increased attention has been given to the use of iontophoresis to deliver drugs and other medicaments through a patient's skin to the desired treatment site. One readily observed benefit is the increased efficacy of the drugs delivered in this fashion. It has become desirable to produce encapsulations of unit doses in easily disposable, non-reusable applicators to be able to control the precise amount of medicament applied. However, an effective nonreusable applicator heretofore has not been available. A low cost, nonreuseable patient application electrode is essential in the treatment of contagious lesions, such as herpes, and helps to prevent further transmission of the disease.
In treating sensitive membranes, such as ear tissue, it is desireable to have an effective and safe way of delivering the medicament without risking harm to the tissue structure from direct electrical contact. It is also desirable to have a malleable or flexible electrode to adapt to each individual patient's ear canal shape and location of treatment. Such an applicator can be used to anaesthesize the tympanic membrane for a clinical myringotomy or for treating the skin in the ear canal.
It is also desireable to be able to treat large areas of the skin with medicament iontophoretically. Typical instances where this need arises is in the treatment of decubitis dermal ulcers or burns or other dermatological conditions, such as psoriasis, eczema or acne. An effective broad area iontophoretic treatment method can avoid more costly alternative treatments, avoid systemic toxicity or side effects, and dramatically increase therapeutic efficacy with lower dosage levels. However, such an applicator must employ an electrode that avoids current flowing along the path of least resistance into a lesion or skin rupture, resulting in a localized burn. This pattern of electrical current flow is also known as tunnelling. The concept of tunnelling combined with the introduction of multichannel electrodes driven by separate current isolated circuits has not been addressed by the prior iontophoretic devices.
These problems are solved in the design of the present invention by providing an improved iontophoretic mediacment applicator that is disposable and non-reusable. The improved iontophoretic applicator may also be suitable for treatment of large areas of skin or specific difficult to treat areas, such as the tympanic membrane.